Various methods and apparatus for packaging and shipping goods have been proposed and implemented in the past. For example, boxes may be stacked onto a pallet and a web of plastic film may be rotated about the pallet load. Such plastic film may be stretched as the plastic film rotates about the pallet load. Alternately, the plastic film may be pre-stretched between rollers prior to being wrapped around the pallet load.
For example, U.S. Pat. No. 5,040,356 relates to a method for stretching plastic which involves a stretching device incorporated into a stretch wrap machine for producing stretched plastic for wrapping a load. Means are provided for stretching a sheet of stretchable plastic material at an angle across one or more stretching devices. The method comprises stretching the plastic over a plurality of generatrices in substantially parallel arrangement, moving the generatrices in an eccentric path about a central axis and moving the generatrices in the axial directions in staggered coordination.
Moreover, U.S. Pat. No. 5,016,427 provides a process for feeding packaging film to a wrapping machine. The film is fed to an upstream and downstream main roller defining between them a passage. As the film is fed towards the rollers, upstream and downstream guide rollers are located at positions nearest the entry and exit sides of the passage.
Hand-held devices for dispensing plastic film for wrapping stacked items have also been used in the past as described in U.S. Pat. No. 4,166,589. Such hand actuated devices include braking mechanisms to stretch the film as it winds around a stack.
Furthermore, U.S. Pat. No. 5,003,752 relates to a plastic film which is stretched breadthwise and longitudinally just before it is wound around a load for wrapping. Stretching of the film is performed by passing the film between stretching rolls each having alternate peripheral ridges and grooves and arranging such that the ridges on each roll mesh with the grooves on the other roll.
Finally, U.S. Pat. No. 4,499,706 teaches a double layer thermal plastic film which is used in pass through stretch wrapping of goods. The double layer improves the tear resistance and puncture resistance of the film.
Moreover, various attempts have heretofore been made to pre-stretch a web of plastic material and rolling said stretched or pre-stretched film around a core for later use. Such stretched rolls of film could be advantageously used by either manually applying the stretched film in a manner disclosed in U.S. Pat. No. 4,166,589 or by applying same by automated means such as a machine or the like. The use of a roll of stretched film could be cost effectively utilized in a pallet wrapping machine by obviating the need for expensive pre-stretched carriages such as that disclosed in U.S. Pat. No. 4,628,667.
However, previous attempts to produce rolls of stretched plastic materials which may later be used to wrap pallet loads including those described above have found limited utility for a number of reasons including:
(a) the film which is stretched has a tendency to retain a "memory" which tends to cause the stretched film to contract into its original length as the film recovers. Accordingly, film which has been stretched and then rolled tends to "weld" together making it difficult to unwrap stretched rolled film without ripping same; PA1 (b) furthermore, stretched film which has been rolled tends to tear easily since such film is under tension and may be easily torn by nicking or stressing the edges of the rolled film.
It is an object of this invention to provide an improved roll of stretched film which is easier to unwind when required to wrap pallet loads and which has strengthened tear characteristics than that presently available by the prior art.
It is also an object of this invention to provide apparatus and a method for producing stretched film which is simple to construct.